The present invention is generally related to control systems for variable speed electric motors, and more particularly, to power modules in such control systems.
Presently, electronic controllers are typically designed for 12 V or 24 V electrical systems such as those used in automotive applications. Electronic controllers in automobiles are typically attached to dashboards, seat bottoms, rear side of the passenger compartment, or the like by being screwed into designated place(s).
Present-day electric motors, such as those used in heating, ventilating, and air conditioning (HVAC) systems of automobiles, are controlled mainly using switch-mode technology, in which a fixed DC power supply is switched on and off with a predetermined switch frequency and pulse width modulated switch-on time as needed to control the motor speed. In the United States, the motor control technology has been implemented primarily by use of a resistive divider (e.g., blower resistor) or by the switch-mode pulse width modulation (PWM). A resistive divider operates by modulating the power provided to the electric motor by a constant or adjustable amount, resulting in a choppy or stepwise level of control.
Alternatively, some use has been made in Europe of a type of linear motor controller with speed set-point inputs in PWM type controller, e.g., the linear current threshold motor controllers shown in U.S. Pat. No. 5,781,385 to Permuy issued on Jul. 14, 1998 or the linear speed controller through motor r.p.m. feedback control shown in U.S. Pat. No. 5,747,956 to Lamm issued May 5, 1998. A PWM set-point signal is used directly for driving the controller switch device through a low-pass filter. A linear electric motor controller generally works by directly controlling the motor speed by setting the voltage feeding to the electric motor. The speed of the electric motor has a linear relationship with the voltage supplied to the motor, hence the term “linear.” These systems tend to be characterized by an undesirably large latency period, i.e., the period between detection and correction of the desired motor speed. In some known systems, digital circuits have been implemented to provide a linear motor controller. Examples of such systems are illustratively shown in U.S. Patent Publication No. US 2003/0063900 A1 of Wang et al., which is hereby incorporated herein in its entirety by express reference thereto.
Known techniques for implementing linear power modules or implementing systems that use linear power modules (e.g., HVAC systems) have sometimes been found to be inadequate in suitably meeting various needs such as efficiency, noise reduction, simplicity in design, cost of production, responsiveness, etc.